Complement Component C1S

C1S products: proteins, antibodies, genes, ELISAs

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More Complement Component C1

Complement Component C1: C1S Background

The complement system is made up of more than 20 different plasma proteins that are sequentially activated through the classical or alternative pathways. Activation by either pathway leads to the generation of activated C3, to the formation of a membrane-attack complex which is responsible for lysis of the target cells, and to the generation of proteolytic fragments that have anaphylatoxin activity.

The first step in the activation of the classical pathway is brought about by the interaction of the C1 complex with antibody-antigen complexes or antibody bound to the surface antigens of target cells. The C1 complex is made up of three subcomponents: C1q, a molecule of unusual structure having six collagen-like stalks coming together at one end to form a short section of fibril, and six globular heads to which the CH2 domain of immunoglobulins can bind. C1r and C1s, two similar molecules occurring in the ratio of 1:2:2 in the C1q:C1r:C1s complex, with structures similar to many of the coagulation and fibrinolytic enzymes in having zymogen structures that are converted to active proteolytic enzymes during activation. Activation of the C1 complex is still poorly understood, with little direct evidence to elucidate the interaction of the subcomponents in the complex. Initially the active form of C1r is generated by an apparently autocatalytic process and this then activates C1s, which then cleaves C2 and C4 to continue the activation process. Active forms of C1r and C1s can be distinguished from the zymogens (Mr=85000) by their two-chain structure, with the serine proteinase activity associated with the smaller (Mr=27000) C-terminal chain which is disulphide-bridged to the larger (Mr=58000) Nterminal chain. Once activated, C1r and C1s can be inhibited by forming a stoichiometric complex with C1 inhibitor, a molecule that has a typical "serpin" type of structure. C1 inhibitor is also thought to control activation of C1 while C1r and C1s are still in the zymogen form.

Complement Component C1: C1S Reference

1. MacKinnon C M, et al. (1987). Molecular cloning of cDNA for human complement component C1s. European Journal of Biochemistry, 169(3), 547-553.
2. Busby W H, et al. (2000). The complement component C1s is the protease that accounts for cleavage of insulin-like growth factor-binding protein-5 in fibroblast medium. Journal of Biological Chemistry, 275(48), 37638-37644.
3. NISSEN M H, et al. (1990). Limited proteolysis of β2‐microglobulin at Lys‐58 by complement component C1s. European Journal of Biochemistry, 189(2), 423-429.

Complement System
Complement System Overview
Complement System Component / Protein Regulator and Receptor
Complement Component / Protein of Complement System+
- Complement Component C1
Complement Component C1R
Complement Component C1S
Complement Component C1Q
Complement Component C1Q: C1QA
Complement Component C1Q: C1QB
Complement Component C1Q: C1QBP
Complement Component C1Q: C1QC
- Complement Component C2
- Complement Component C5
- Complement Component C6
- Complement Component C7
- Complement Component C8
- Complement Component C9
- Complement Component Factor B/CFB
- Complement Component Factor D/CFD/Adipsin
- Complement Component Factor Properdin/CFP
Complement Genetic Feature
Complement Activation Pathways
Complement System Role
Complement System and Diseases
Complement System Deficiency Diseases
Complement System Structure
Complement System Effector Functions
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